The present invention relates to a hexagonal 2-dimensional reflection phase grating diffuser. Sound diffusers described thus far in the patent literature have included single plane devices, for example, those disclosed in U.S. Pat. No. D291,601 to D'Antonio et al. and U.S. Pat. No. 4,821,839 to D'Antonio et al. They cause scattering into a hemi-disc, acting as a plane surface in the other directions. While this is the preferred diffuser design for some applications, there is a need for a diffuser that scatters into a hemisphere.
For a Schroeder diffuser this can be achieved by forming a two-plane device, often referred to as a 2D diffuser. This device scatters optimally in the x- and z-direction, and therefore gives even lobes on a hemisphere. Examples include U.S. Pat. No. D306,764 to D'Antonio et al., U.S. Pat. No. 5,401,921 to D'Antonio et al., and U.S. Pat. No. 5,817,992 to D'Antonio. All of these devices have been based on orthogonal designs, based on a rectangular grid. The teachings of this patent will describe a novel 2D diffuser, based on a hexagonal grid.
The present invention consists of a hexagonally shaped device consisting of wells made of smaller hexagonal shapes, and represents a significant step in the evolution of diffusing devices because it is better suited than existing devices for solving acoustical issues in certain types of architectural structures. The present invention includes significant improvements that are not available in currently available products.
For accurate stereo monitoring, it is important to establish a symmetrical listening triangle, two vertices of which are established by the theoretical point sources of the two monitors, and the third vertex being a point just behind the listener's head. The equilateral listening triangle is usually the most advantageous configuration since it provides an excellent balance between a wide stereo sound field and a stable center (or phantom) image.
In a well-designed control room, this listening triangle is one of the core elements that determines the interrelationships between all of the other elements of the room. This equilateral listening triangle, seen in FIG. 1, is made up of three sides, each representing an axis of symmetry rotated 120 degrees from the other two, and thus introduces an element of tri-axial rather than bi-axial layout into the control room plan.
The reflection free zone (RFZ) control room principle was first developed by Dr. Peter D'Antonio in 1983, for the purpose of creating the most accurate monitoring possible at the recording engineer's listening position. This is accomplished by eliminating early reflections at the engineer's position by angling the walls in such a way that all such reflections are channeled past the ends of the recording console and toward the back of the room. Any subsequent secondary reflections re-entering the engineer's sound field from the rear of an adequately sized RFZ control room are delayed by more than 20 ms, and usually scattered by rear wall diffusers, and are clearly perceived as ambience separate from the direct sound, rather than causing comb filtering as happens when specular reflections earlier than 20 ms are allowed to blend with the direct sound.
Comb filtering causes serious deterioration of perceived sound quality and makes it impossible for the engineer to reliably trust the frequency spectrum and sound quality of the music.
D'Antonio's plan of an RFZ control room was published on page 302 of The Master Handbook of Acoustics 2nd. ed. by F. A. Everest, TAB Books, 1989, and shows a configuration suggestive of a half-hexagon within the main three walls of the front of the control room, with the monitor soffits set symmetrically in the vertices of the 120 degree angles formed by those three walls. Since the 1980s, experience has shown the hexagonal configuration in the front of the room to be the most advantageous RFZ shape for a variety of room sizes, maximizing the size of the reflection free zone for the engineer, while using space economically. The front end of the room is where the hexagonal shape is most important, since the purposeful reflection of direct sound from the monitors takes place in the front of the room. The angles of rear side walls are less important from a reflection standpoint. Note that in addition to the listening triangle mentioned above, it is seen that another important element of a good monitoring room—the shape of the room itself—relies upon tri-axial rather than bi-axial layout.